//滚动监听INterSectionObserver
const observer = new IntersectionObserver(entries => {
    entries.forEach(entry => {
        if (entry.isIntersecting) {
            entry.target.classList.add("actived")
        } else {
            entry.target.classList.remove("actived")
        }
    })
})
const hiddenElement = document.querySelectorAll(".flag")
hiddenElement.forEach(el => observer.observe(el))
